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Org. Synth. 1925, 4, 59
DOI: 10.15227/orgsyn.004.0059
n-PROPYLBENZENE
[Benzene, propyl-]
Submitted by Henry Gilman and W. E. Catlin.
Checked by C. S. Marvel and H. R. Snyder.
1. Procedure
In a dry 3-l. flask, fitted with a mercury-sealed stirrer, a 500-cc. dropping funnel, and a condenser provided at its upper end with a drying tube containing a mixture of calcium chloride and soda-lime (Note 1), is placed 48.6 g. (2 atoms) of magnesium turnings. There are then added 200 cc. of dry ether, a small crystal of iodine, and about 25 cc. of a solution of 253 g. (230 cc., 2 moles) of freshly distilled benzyl chloride in 1 l. of dry ether. If the reaction does not start at once, the flask is partially immersed in a bath containing water heated to about 40°. As soon as the ether begins to boil, and reaction sets in, the bath is removed and stirring is commenced. The remainder of the benzyl chloride in ether can be added during the course of one-half hour if the reaction is regulated by cooling the greater part of the flask by immersion in ice water (Note 2). The reaction will continue for about fifteen minutes after all the benzyl chloride has been added, and then the mixture is refluxed gently for about fifteen minutes.
To the stirred benzylmagnesium chloride is then added 616 g. (522 cc., 4 moles) of freshly distilled diethyl sulfate (Note 3). The addition of diethyl sulfate is so regulated that gentle refluxing takes place throughout the reaction. Once reaction is started with a few cubic centimeters of diethyl sulfate, it is necessary to cool the reaction flask by ice water in order to complete addition within about one hour. When all the ester has been added, stirring is continued with gentle boiling for fifteen minutes (Note 4).
The cooled mixture is next poured, with stirring, upon a mixture of 1 kg. of crushed ice, 1 l. of water, and 200 cc. of concentrated hydrochloric acid. After stirring a few minutes to dissolve the sludge, the major part of the water layer is siphoned off and the ethereal solution is separated. The water layer is washed once with about 50 cc. of ether, and this washing is added to the ethereal solution of n-propylbenzene. The ether is removed by distillation from a water or steam bath through a fractionating column. The residue is poured into 1 l. of 10 per cent sodium hydroxide solution in about 50 per cent alcohol, and this mixture is refluxed for one hour (Note 5). After the n-propylbenzene is thrown out by the addition of a large volume of water, the hydrocarbon is separated, combined with an ether extract of the aqueous layer, dried by standing over 10–15 g. of solid potassium hydroxide, and fractionally distilled through an efficient column. The yield of n-propylbenzene, distilling at 155–160°, is 165–180 g. (70–75 per cent of the theoretical amount).
2. Notes
1. The function of the calcium chloride and soda-lime is to absorb any moisture and carbon dioxide which might diffuse into the reaction flask. The deleterious effect of another constituent of the atmosphere, oxygen, may be decreased by first sweeping out the flask with dry nitrogen or hydrogen. The initial use of a dry inert atmosphere may also be supplemented by the use of a trap1 to exclude the air, particularly in those operations requiring extensive periods.
2. Benzylmagnesium chloride is one of a group of Grignard reagents which can be prepared in satisfactory yields by the rapid addition of the halide to magnesium in ether.2
3. If the diethyl sulfate is dark in color it should be washed, prior to distillation, with ice water and then with a sodium bicarbonate solution until all free acid is removed.
4. At the end of this time a negative color test shows that the Grignard reagent has been used up.
5. The solution is refluxed with alcoholic alkali to decompose any unaltered diethyl sulfate.
3. Discussion
n-Propylbenzene can be prepared by the action of sodium on propylbromide and bromobenzene;3 by the action of diethylzinc4 or ethylmagnesium bromide5 on benzyl chloride; by the action of diethyl sulfate6 or ethyl p-toluenesulfonate7 on benzylmagnesium chloride; and by the reduction of ethyl phenyl ketone,8 methyl benzyl ketone,8 or propenylbenzene.9 Propylbenzene can also be obtained from benzene by a variety of alkylation processes: With cyclopropane and aluminum chloride10 or hydrogen fluoride;11 with propylene and phosphorus pentoxide;12 with propyl bromide and aluminum chloride;13 and with propyl alcohol and aluminum chloride14 or sulfuric acid.15
This preparation is referenced from:

References and Notes
  1. Gilman and Hewlett, Rec. trav. chim. 48, 1124 (1929).
  2. Gilman, Zoellner and Dickey, J. Am. Chem. Soc. 51, 1583 (1929).
  3. Fittig, Schaeffer and König, Ann. 149, 324 (1869).
  4. Schiff, Ber. 10, 294 (1877); Paterno and Spica, Gazz. chim. ital. 7, 21 (1877)
  5. Bert, Compt. rend. 186, 587 (1928).
  6. Gilman and Hoyle, J. Am. Chem. Soc. 44, 2621, 2969 (1922).
  7. Gilman and Beaber, ibid. 47, 523 (1925).
  8. Willgerodt and Scholtz, J. prakt. Chem. (2) 81, 387 (1910); Clemmensen, Ber. 46, 1839 (1913); Schmidt, Hopp, and Schoeller, Ber. 72, 1893 (1939).
  9. Klages, Ber. 36, 622 (1903); Kunckell and Dettmar, Ber. 36, 773 (1903).
  10. Grosse and Ipatieff, J. Org. Chem. 2, 447 (1937).
  11. Simons, Archer, and Adams, J. Am. Chem. Soc. 60, 2955 (1938).
  12. Truffault, Compt. rend. 202, 1286 (1936).
  13. Heise, Ber. 24, 768 (1891); Konovalov, J. Russ. Phys. Chem. Soc. 27, 457 (1895) [Bull. soc. chim. (3) 16, 864 (1896)].
  14. Tsukervanik and Vikhrova, J. Gen. Chem. (U.S.S.R.) 7, 632 (1937) [C. A. 31, 5779 (1937)].
  15. Brochet and Boulenger, Compt. rend. 117, 236 (1893).

Appendix
Chemical Abstracts Nomenclature (Collective Index Number);
(Registry Number)

ester

soda-lime

hydrocarbon

alcohol (64-17-5)

calcium chloride (10043-52-4)

sulfuric acid (7664-93-9)

hydrochloric acid (7647-01-0)

Benzene (71-43-2)

ether (60-29-7)

hydrogen (1333-74-0)

sodium hydroxide (1310-73-2)

sodium bicarbonate (144-55-8)

magnesium,
magnesium turnings (7439-95-4)

propylene (115-07-1)

propylbromide,
Propyl bromide (106-94-5)

oxygen (7782-44-7)

nitrogen (7727-37-9)

carbon dioxide (124-38-9)

hydrogen fluoride (7664-39-3)

iodine (7553-56-2)

aluminum chloride (3495-54-3)

potassium hydroxide (1310-58-3)

sodium (13966-32-0)

benzyl chloride (100-44-7)

bromobenzene (108-86-1)

propyl alcohol (71-23-8)

benzylmagnesium chloride (6921-34-2)

Benzene, propyl-,
Propylbenzene,
n-PROPYLBENZENE (103-65-1)

diethyl sulfate (64-67-5)

diethylzinc (557-20-0)

ethylmagnesium bromide (925-90-6)

ethyl phenyl ketone (93-55-0)

Methyl benzyl ketone (103-79-7)

propenylbenzene

cyclopropane (75-19-4)

phosphorus pentoxide (1314-56-3)

ethyl p-toluenesulfonate (80-40-0)